Structure providing poly-resistor under shallow trench isolation and above high resistivity polysilicon layer

ABSTRACT

A structure provides a polysilicon resistor under a shallow trench isolation (STI). The structure includes the STI, a resistor in the form of a doped buried polysilicon layer under the STI, and a high resistivity (HR) polysilicon layer under the doped buried polysilicon layer. The structure also includes a pair of contacts operatively coupled in a spaced manner to the doped buried polysilicon layer. A related method is also disclosed.

BACKGROUND

The present disclosure relates to integrated circuits (IC), and morespecifically, to a structure providing a polysilicon resistor under ashallow trench isolation (STI) and above a high resistivity polysiliconlayer.

Resistors for an IC are oftentimes formed in inter-layer dielectric(ILD) layers above the transistors. These layers are referred to asmiddle-of-line (MOL) layers and back-end-of-line (BEOL) layers. MOLlayers are just above the front-end-of-line (FEOL) layers that includethe transistors, and BEOL layers are above the MOL layers. Both MOL andBEOL layers provide scaling interconnects for the IC. The resistors areoftentimes formed over an oxide or STI, which reduces thermaldissipation from the resistor into the substrate. For polysiliconresistors placed on the surface of a substrate, e.g., over STI,resistance variation due to temperature under high current is also aconcern. In addition, the resistors extend horizontally within thelayers, taking up valuable area and potentially blocking access to otherfunctional components therebelow, requiring complex electricalconnections to those components, or addition of more components notcovered by the resistor.

SUMMARY

One aspect of the disclosure includes a structure, comprising: a shallowtrench isolation (STI); a doped buried polysilicon layer under the STI;a high resistivity (HR) polysilicon layer under the doped buriedpolysilicon layer; and a pair of contacts operatively coupled in aspaced manner to the doped buried polysilicon layer.

Another aspect of the disclosure is directed to a structure, comprising:a shallow trench isolation (STI); a resistor including a doped buriedpolysilicon layer under the STI; a high resistivity (HR) polysiliconlayer under the resistor; and a pair of contacts operatively coupled ina spaced manner to the resistor, wherein the HR polysilicon layerincludes a noble dopant, and wherein the doped buried polysilicon layerincludes a boron dopant.

Another aspect of the disclosure includes an aspect of the disclosurerelated to a method, comprising: forming a shallow trench isolation(STI) in a substrate; doping the substrate with a noble dopant, forminga disordered crystallographic layer under the STI; converting thedisordered crystallographic layer to a doped buried polysilicon layerunder the STI and a high resistivity (HR) polysilicon layer under thedoped buried polysilicon layer; and forming a pair of contactsoperatively coupled in a spaced manner to the doped buried polysiliconlayer.

The foregoing and other features of the disclosure will be apparent fromthe following more particular description of embodiments of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of this disclosure will be described in detail, withreference to the following figures, wherein like designations denotelike elements, and wherein:

FIG. 1 shows a cross-sectional view of a structure including apoly-resistor, according to embodiments of the disclosure.

FIG. 2 shows a plan view of the structure of FIG. 1 (see view line 1-1)including the poly-resistor, according to embodiments of the disclosure.

FIG. 3 shows a cross-sectional view of a structure including apoly-resistor, according to other embodiments of the disclosure.

FIG. 4 shows a cross-sectional view of a structure including apoly-resistor, according to yet other embodiments of the disclosure.

FIG. 5 shows a cross-sectional view of a preliminary structure for amethod, according to embodiments of the disclosure.

FIG. 6 shows a cross-sectional view of introducing a noble dopant toform a disordered crystallographic layer, according to embodiments ofthe disclosure.

FIG. 7 shows a cross-sectional view of converting the disorderedcrystallographic layer of FIG. 6 to a doped buried polysilicon layerunder an STI and a high-resistivity (HR) polysilicon layer under thedoped buried polysilicon layer, according to embodiments of thedisclosure.

FIG. 8 shows a cross-sectional view of introducing a first dopant toform contacts for the poly-resistor, according to embodiments of thedisclosure.

FIG. 9 shows a cross-sectional view of introducing a second dopant toform contacts for the poly-resistor, according to embodiments of thedisclosure.

FIG. 10 shows a cross-sectional view of introducing a noble dopant toform a disordered crystallographic layer, according to other embodimentsof the disclosure.

FIG. 11 shows a cross-sectional view of converting the disorderedcrystallographic layer of FIG. 10 to a doped buried polysilicon layerunder an STI and an HR polysilicon layer under the doped buriedpolysilicon layer, according to other embodiments of the disclosure.

FIG. 12 shows a cross-sectional view of introducing a dopant to formcontacts for the poly-resistor, according to embodiments of thedisclosure.

FIG. 13 shows a cross-sectional view of introducing a noble dopant toform a disordered crystallographic layer, according to yet otherembodiments of the disclosure.

It is noted that the drawings of the disclosure are not necessarily toscale. The drawings are intended to depict only typical aspects of thedisclosure, and therefore should not be considered as limiting the scopeof the disclosure. In the drawings, like numbering represents likeelements between the drawings.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part thereof, and in which is shown by way ofillustration specific illustrative embodiments in which the presentteachings may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice thepresent teachings, and it is to be understood that other embodiments maybe used and that changes may be made without departing from the scope ofthe present teachings. The following description is, therefore, merelyillustrative.

It will be understood that when an element such as a layer, region, orsubstrate is referred to as being “on” or “over” another element, it maybe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there may be no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it maybe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present disclosure, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present disclosure. Thus, the phrases “in one embodiment” or “inan embodiment,” as well as any other variations appearing in variousplaces throughout the specification are not necessarily all referring tothe same embodiment. It is to be appreciated that the use of any of thefollowing “/,” “and/or,” and “at least one of,” for example, in thecases of “A/B,” “A and/or B” and “at least one of A and B,” is intendedto encompass the selection of the first listed option (A) only, or theselection of the second listed option (B) only, or the selection of bothoptions (A and B). As a further example, in the cases of “A, B, and/orC” and “at least one of A, B, and C,” such phrasing is intended toencompass the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B), or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in the art, for as many items listed.

Embodiments of the disclosure provide a structure that provides apolysilicon resistor (poly-resistor) under a shallow trench isolation(STI). The structure includes the STI, a resistor in the form of a dopedburied polysilicon layer under the STI, and a high resistivity (HR)polysilicon layer under the doped buried polysilicon layer. Thestructure also includes a pair of contacts operatively coupled in aspaced manner to the doped buried polysilicon layer. A related method isalso disclosed. The structure eliminates oxide/STI under the resistor,which improves the resistor's thermal dissipation to the substrate. Thestructure also allows improved resistor density (with reduced area) byallowing stacked poly-resistors below the STI and above the STI. The HRpolysilicon layer provides an isolation region beneath the poly-resistorthat diminishes parasitic leakage of active devices to the substrate. Inthis setting, the HR polysilicon layer also provides thermalconductivity from the poly-resistor with reduced substrate coupling, andimproved frequency response.

FIG. 1 shows a cross-sectional view of a structure 100 according toembodiments of the disclosure. Structure 100 is formed over a substrate102. As illustrated, embodiments of the disclosure may be implemented ona bulk semiconductor substrate 104. However, the teachings of thedisclosure may also be implemented on other substrates such as asemiconductor-on-insulator (SOI) substrate (not shown). SOI substratesinclude a layered semiconductor-insulator-semiconductor substrate inplace of a more conventional bulk semiconductor substrate. SOIsubstrates include a semiconductor-on-insulator (SOI) layer over aburied insulator layer over a base semiconductor layer. Semiconductorsubstrate 104 may include but is not limited to silicon, germanium,silicon germanium, silicon carbide, and those consisting essentially ofone or more III-V compound semiconductors having a composition definedby the formula Al_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), whereX1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions, eachgreater than or equal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being thetotal relative mole quantity). Other suitable substrates include II-VIcompound semiconductors having a compositionZn_(A1)Cd_(A2)Se_(B1)Te_(B2), where A1, A2, B1, and B2 are relativeproportions each greater than or equal to zero and A1+A2+B1+B2=1 (1being a total mole quantity). Where an SOI substrate is employed, theSOI layer and base semiconductor layer may include any of theafore-mentioned semiconductor materials. Furthermore, a portion orentire substrate 102 may be strained. In any event, semiconductorsubstrate 104 may be provided as an amorphous semiconductor material,e.g., with no wells.

Structure 100 also includes a shallow trench isolation (STI) 110. STI110 includes a trench 112 etched into substrate 102 and filled with aninsulating material 114. In certain embodiments, STI 110 may isolate oneregion of the substrate from an adjacent region of the substrate. Forexample, STI 110 may electrically isolate one active region 120 fromanother active region 122. One or more transistors (not shown) of agiven polarity may be disposed within an area isolated by STI 110.Insulating material 114 may include any currently-known or laterdeveloped substance for providing electrical insulation, and as examplesmay include: silicon nitride (Si₃N₄), silicon oxide (SiO₂), fluorinatedSiO₂ (FSG), hydrogenated silicon oxycarbide (SiCOH), porous SiCOH,boro-phospho-silicate glass (BPSG), silsesquioxanes, carbon (C) dopedoxides (i.e., organosilicates) that include atoms of silicon (Si),carbon (C), oxygen (O), and/or hydrogen (H), thermosetting polyaryleneethers, a spin-on silicon-carbon containing polymer material, nearfrictionless carbon (NFC), or layers thereof.

As noted, typical poly-resistors (not shown) may be formed over STI 110in an inter-layer dielectric (ILD) layer 124 thereover. In this case,STI 110 limits heat dissipation into substrate 102. Suitable dielectricmaterials for ILD layer 124 may include but are not limited to:carbon-doped silicon dioxide materials; fluorinated silicate glass(FSG); organic polymeric thermoset materials; silicon oxycarbide; SiCOHdielectrics; fluorine doped silicon oxide; spin-on glasses;silsesquioxanes, including hydrogen silsesquioxane (HSQ), methylsilsesquioxane (MSQ) and mixtures or copolymers of HSQ and MSQ;benzocyclobutene (BCB)-based polymer dielectrics, and anysilicon-containing low-k dielectric. Examples of spin-on low-k filmswith SiCOH-type composition using silsesquioxane chemistry include HOSP™(available from Honeywell), JSR 5109 and 5108 (available from JapanSynthetic Rubber), Zirkon™ (available from Shipley Microelectronics, adivision of Rohm and Haas), and porous low-k (ELk) materials (availablefrom Applied Materials). Examples of carbon-doped silicon dioxidematerials, or organosilanes, include Black Diamond™ (available fromApplied Materials) and Coral™ (available from Lam Research). An exampleof an HSQ material is FOx™ (available from Dow Corning).

Structure 100 includes a resistor 130 (also referred to herein as“poly-resistor 130”) including a doped buried polysilicon layer 132under STI 110. Doped buried polysilicon layer 132 is denoted as ‘buried’because of its location below an upper surface 134 of substrate 102(same plane as upper surface of STI 110 in FIG. 1 ). Doped buriedpolysilicon layer 132 may include any dopant capable of controlling aresistivity of the layer. In one non-limiting example, doped buriedpolysilicon layer 132 under STI 110 may include a boron (B) dopant.However, it may be doped with other p-type or n-type dopants depending,for example, on the doping in substrate 102 or below a high resistivity(HR) polysilicon layer 140 (described herein) therebelow. Alternativedopants may include but are not limited to: other p-type dopants such asindium (In), aluminum (Al), and/or gallium (Ga), or n-type dopants suchas phosphorous (P), arsenic (As), and/or antimony (Sb). A dopantconcentration in doped buried polysilicon layer 132 may be controlled todictate the resistivity of polysilicon layer 132.

Structure 100 also includes a high resistivity (HR) polysilicon layer140 under doped buried polysilicon layer 132. HR polysilicon layer 140may include a noble dopant capable of changing the crystalline structureof HR polysilicon layer 140 from that of substrate 102, creating aresistivity therein greater than substrate 102 and perhaps higher thandoped buried polysilicon layer 132. The noble dopant may include, forexample, argon (Ar), neon (Ne), krypton (Kr), xenon (Xe), helium (He),or a combination thereof. In one particular embodiment, argon (Ar) isused.

Structure 100 also includes a pair of contacts 144, 146 operativelycoupled in a spaced manner to doped buried polysilicon layer 132.Contacts 144, 146 provide an electrically conductive pathway to resistor130. In FIG. 1 , each contact 144, 146 includes a doped monocrystallinesemiconductor material 150 extending beside STI 110. That is, dopedmonocrystalline semiconductor material 150 is in substrate 102 andextends vertically along lateral sides 151 of STI 100. As shown in FIG.1 , each contact 144, 146 is operatively coupled to a lateral end 152 ofdoped buried polysilicon layer 132. Also, each contact 144, 146 contactsan upper surface 154 of HR polysilicon layer 140. Doped monocrystallinesemiconductor material 150 may include a p-type or n-type dopantdepending on, for example, the type of active devices formed elsewherein active regions 120, 122. N-type dopants may include but are notlimited to: phosphorous (P), arsenic (As), antimony (Sb). N-type is anyelement introduced to semiconductor to generate free electron (by“donating” electron to semiconductor); and must have one more valanceelectron than semiconductor. P-type dopants may include but are notlimited to: boron (B), indium (In) and gallium (Ga). P-type is anyelement introduced to semiconductor to generate free hole (by“accepting” electron from semiconductor atom and “releasing” hole at thesame time); and the acceptor atom must have one valence electron lessthan host semiconductor. An upper layer 158 of contacts 144, 146 mayhave a higher dopant concentration than doped monocrystallinesemiconductor material 150. Any now known or later developed form ofmetal contact or wire 160 may be formed through ILD layer 124 tocomplete contacts 144, 146.

FIG. 2 shows a plan view of structure 100. As shown in FIGS. 1 and 2 ,structure 100 may also include an isolation ring 170 bounding dopedburied polysilicon layer 132. Isolation region 170 may include any nowknown or later developed electrical isolation structure. For example,isolation ring 170 may include a trench isolation or a doped well. Wherea doped well is used, it will have a different polarity than contacts144, 146, e.g., an n-well where doped monocrystalline semiconductormaterial 150 is doped with a p-type dopant. Where isolation ring 170includes a trench isolation, it may include an STI, a deep trenchisolation (DTI, as shown) or a dual STI. When in the form of a trenchisolation, isolation ring 170 may be formed similarly to STI 110.

For purposes that will be described relative to methods herein,structure 100 may also optionally include a retarding implant region 174(dashed line) within and/or below HR polysilicon layer 140, i.e., belowHR polysilicon layer 140, within HR polysilicon layer 140, or bothwithin and below HR polysilicon layer 140. Retarding implant region 174may include any dopant capable of retarding the depletion of otherdopants, such as boron (B) in resistor 130, beyond HR polysilicon layer140 into substrate 102. In one non-limiting example, the dopant mayinclude carbon (C).

FIG. 3 shows a cross-sectional view of structure 100 according toanother embodiment of the disclosure. Structure 100 in FIG. 3 issubstantially similar to that shown in FIGS. 1 and 2 , except dopedburied polysilicon layer 132 and contacts 144, 146 are different. InFIG. 3 , doped buried polysilicon layer 132 includes a pair of verticalportions 180, 182 extending vertically along lateral sides 151 of STI110. That is, the material and dopant in vertical portions 180, 182matches that of doped buried polysilicon layer 132 in contrast tomaterial 150 in FIGS. 1 and 2 , which includes other dopants. In thismanner, as observed in FIG. 3 , resistor 130 and doped buriedpolysilicon layer 132 may have a U-shaped cross-section. Each contact144, 146 in FIG. 3 may include a doped semiconductor material 184operatively coupled to an upper surface 186 of a respective verticalportion 180, 182 of doped buried polysilicon layer 132. The dopant indoped semiconductor material 184 may be the same as in other areas ofactive regions 120, 122 (into or out of page). Any now known or laterdeveloped form of metal contact or wire 160 may be formed through ILDlayer 124 to complete contacts 144, 146, i.e., doped semiconductormaterial 184.

FIG. 4 shows a cross-sectional view of structure 100, according to yetanother embodiment. Structure 100 in FIG. 4 is substantially similar tothat shown in FIGS. 1 and 2 , except doped buried polysilicon layer 132and contacts 144, 146 are different from that shown in FIGS. 1 and 3 .In FIG. 4 , each contact 144, 146 extends through STI 110 to an uppersurface 188 of doped buried polysilicon layer 132. Here, contacts 144,146 may include any now known or later developed form of metal contactor wire (similar to 160 in other embodiments) and may be formed throughILD layer 124 and STI 110 to land directly on doped buried polysiliconlayer 132, i.e., resistor 130.

As will be recognized, where STI 110 forms spaced active regions 120,122, a distance between active regions 120, 122 in FIGS. 1-4 may controla spacing between contacts 144, 146. In this manner, the length ofresistor 130 and the resistance provided by resistor 130 can be furthercontrolled.

Referring to FIGS. 5-13 , methods of forming structure 100 according tovarious embodiments will be described. FIG. 5 shows a preliminarystructure 200, and the forming of STI 110 in substrate 102. As noted,STI 110 may isolate a pair of spaced active regions 120, 122. STI 110may be formed using any now known or later developed process, e.g.,patterning a mask (not shown), etching openings into substrate 102,filling the openings with insulating material 114 (as listed herein),and planarizing. Etching generally refers to the removal of materialfrom a substrate (or structures formed on the substrate), and is oftenperformed with a mask in place so that material may selectively beremoved from certain areas of the substrate, while leaving the materialunaffected, in other areas of the substrate. There are generally twocategories of etching, (i) wet etch and (ii) dry etch. Wet etch isperformed with a solvent (such as an acid) which may be chosen for itsability to selectively dissolve a given material (such as oxide), while,leaving another material (such as polysilicon) relatively intact. Thisability to selectively etch given materials is fundamental to manysemiconductor fabrication processes. A wet etch will generally etch ahomogeneous material (e.g., oxide) isotropically, but a wet etch mayalso etch single-crystal materials (e.g. silicon wafers)anisotropically. Dry etch may be performed using a plasma. Plasmasystems can operate in several modes by adjusting the parameters of theplasma. Ordinary plasma etching produces energetic free radicals,neutrally charged, that react at the surface of the wafer. Since neutralparticles attack the wafer from all angles, this process is isotropic.Ion milling, or sputter etching, bombards the wafer with energetic ionsof noble gases which approach the wafer approximately from onedirection, and therefore this process is highly anisotropic.Reactive-ion etching (RIE) operates under conditions intermediatebetween sputter and plasma etching and may be used to produce deep,narrow features, such as STI 110 openings/trenches. Preliminarystructure 200 also includes a pad nitride layer 202 over a pad oxidelayer 204 in active regions 120, 122, each of which may be formed usingany now known or later developed process.

FIGS. 6-9 show cross-sectional views of steps of forming structure 100of FIG. 1 . FIG. 6 shows a cross-sectional view of the structure afterhaving optionally removed pad nitride layer 202, exposing pad oxidelayer 204. Pad nitride layer 202 may be removed using any appropriateetching process, e.g., a hot phosphorous process. FIG. 6 also showsoptionally doping to form a retarding implant region 174, which willultimately be located within and/or below HR polysilicon layer 140. Anyform of a mask 208 may be formed to direct the doping. Mask 208 may beany mask material patterned to form HR polysilicon layer 140, e.g.,where shown in FIG. 6 and perhaps other active regions of the IC.Retarding implant region 174 may be formed using any now known or laterdeveloped doping process, such as in-situ formation or ion implanting.FIG. 6 also shows doping with a noble dopant, forming a disorderedcrystallographic layer 210 under STI 110 (and pair of spaced activeregions 120, 122, where provided). As noted, the noble dopant mayinclude, for example, argon (Ar), neon (Ne), krypton (Kr), xenon (Xe),helium (He), or a combination thereof. In one particular embodiment,argon (Ar) is used.

FIG. 7 shows converting disordered crystallographic layer 210 (FIG. 6 )to doped buried polysilicon layer 130 under STI 110 and HR polysiliconlayer 140 under doped buried polysilicon layer 130, i.e., after removingmask 208 using any appropriate ashing process. In one embodiment, theconversion can be accomplished by annealing. The anneal can include, forexample, any appropriate rapid thermal process (RTP) and can have anytemperature and/or duration to obtain the desired depth of layers 132,140. Where provided, retarding implant region 174 may limit the extentto which layers 132, 140 extend into substrate 102. Otherwise, thedopant concentrations in layers 132, 140 and the conversion process maycontrol the thicknesses of layer 132, 140. As shown in FIG. 7 , theconversion creates HR polysilicon layer 140, doped buried semiconductorlayer 132, and (recrystallized) monocrystalline semiconductor material212 over doped buried semiconductor layer 132.

FIGS. 8-9 show cross-sectional views of forming a pair of contacts 144,146 operatively coupled in a spaced manner to doped buried polysiliconlayer 132. In FIG. 8 , a mask 220 is formed exposing active regions 120,122. FIG. 8 also shows introducing a dopant into monocrystallinesemiconductor material 212 to form doped monocrystalline semiconductormaterial 150 extending beside STI 110. That is, doped monocrystallinesemiconductor material 150 is in substrate 102 and extends verticallyalong lateral sides 151 of STI 100. The dopant may be introduced in anymanner such as ion implantation. Mask 220 may be removed using anyappropriate ashing process. FIG. 9 shows forming another mask 222exposing active regions 120, 122 and STI 110. Mask 222 may be the sameas that used for doping of source/drain regions (not shown) of activedevices in other regions of the IC. FIG. 8 shows introducing a dopantinto monocrystalline semiconductor material 212 to form upper layer 158of contacts 144, 146 having a higher dopant concentration than dopedmonocrystalline semiconductor material 150. Mask 222 may be removedusing any appropriate ashing process, and ILD layer 124 (FIG. 1 ) formedover the structure. As shown in FIG. 1 , any now known or laterdeveloped form of metal contact or wire 160 may be formed through ILDlayer 124 to complete contacts 144, 146.

FIGS. 10-12 show cross-sectional views for forming structure 100 asillustrated in FIG. 3 . FIG. 10 shows a cross-sectional view with a mask224 formed on the structure, similarly to that illustrated in FIG. 5 .Here, in contrast to FIGS. 6-9 , pad nitride layer 202 remains overactive regions 120, 122. That is, each active region 120, 122 includespad nitride layer 204 thereover during the doping of STI 210 and thespaced active regions 120, 122 with the noble dopant, as will bedescribed. Pad nitride layer 202 prevents recrystallization of verticalportions 180, 182 (FIG. 3 ) beside STI 110. Mask 224 exposes activeregions 120, 122 and STI 110. At this stage, retarding implant region174 may be formed by doping (e.g., ion implantation) to be ultimatelylocated within and/or below HR polysilicon layer 140. However, thisprocess is not shown in FIG. 10 to illustrate the option of omittingthis step. Any form of a mask 224 may be formed to direct the doping.Mask 224 may be any mask material patterned to form HR polysilicon layer140, e.g., where shown in FIG. 10 and perhaps other active regions ofthe IC. FIG. 10 also shows doping with a noble dopant, forming adisordered crystallographic layer 210 under STI 110 (and pair of spacedactive regions 120, 122, where provided). As noted, the noble dopant mayinclude, for example, argon (Ar), neon (Ne), krypton (Kr), xenon (Xe),helium (He), or a combination thereof. In one particular embodiment,argon (Ar) is used.

FIG. 11 shows converting disordered crystallographic layer 210 (FIG. 10) to doped buried polysilicon layer 130 under STI 110 and HR polysiliconlayer 140 under doped buried polysilicon layer 130, i.e., after removingmask 224 (FIG. 10 ) using any appropriate ashing process. In oneembodiment, the conversion can be accomplished by annealing. As noted,the anneal can include, for example, any appropriate rapid thermalprocess (RTP) and can have any temperature and/or duration to obtain thedesired depth of layers 132, 140. Where provided, retarding implantregion 174 (not shown) may limit the extent to which layers 132, 140extend into substrate 102. Otherwise, the dopant concentrations inlayers 132, 140 and the conversion process may control the thicknessesof layer 132, 140. Here, due to the presence of pad nitride layer 202,doped buried polysilicon layer 132 includes vertical portions 180, 182extending vertically along lateral sides 152 of STI 110 in each activeregion 120, 122. Hence, the conversion creates HR polysilicon layer 140,doped buried semiconductor layer 132, and vertical portions 180, 182 ofdoped buried semiconductor layer 132 extending along lateral sides 151of STI 110.

FIG. 12 shows a cross-sectional view of removing pad nitride layer 202,e.g., with a hot phosphorous process. FIG. 12 also shows forming pair ofcontacts 144, 146 by forming a doped polycrystalline semiconductormaterial 184 operatively coupled to upper surface 186 of verticalportion 180, 182 of doped buried polysilicon layer 132 in each activeregion 120, 122. More particularly, FIG. 12 shows forming a mask 230 andintroducing a dopant to form doped polycrystalline semiconductormaterial 184, e.g., by ion implantation through pad oxide layer 204.FIG. 3 shows structure 100, after removing mask 230, and forming metalcontacts or wires 160 through ILD layer 124 and pad oxide layer 204(FIG. 12 ) to complete contacts 144, 146, as described herein.

FIG. 13 shows a cross-sectional view of forming structure 100 asillustrated in FIG. 4 . The FIG. 4 embodiment does not include activeregions 120, 122. In this case, structure 100 may be formed with lesssteps than the FIGS. 1 and 3 embodiments. FIG. 13 shows an optional mask240 exposing STI 110. At this stage, retarding implant region 174 (notshown) may be optionally formed by doping (e.g., ion implantation).However, this process is not shown in FIG. 13 to illustrate the optionof omitting this step. Any form of mask 240 may be formed to direct thedoping. For example, mask 240 may be any mask material patterned to formHR polysilicon layer 140, e.g., where shown in FIG. 4 and perhaps otheractive regions of the IC. FIG. 13 also shows doping with a noble dopant,forming a disordered crystallographic layer 210 under STI 110. As noted,the noble dopant may include, for example, argon (Ar), neon (Ne),krypton (Kr), xenon (Xe), helium (He), or a combination thereof. In oneparticular embodiment, argon (Ar) is used.

FIG. 4 shows converting disordered crystallographic layer 210 (FIG. 13 )to doped buried polysilicon layer 130 under STI 110 and HR polysiliconlayer 140 under doped buried polysilicon layer 130, i.e., after removingmask 240 (FIG. 13 ) using any appropriate ashing process. As noted, theconversion can be accomplished by annealing, as described herein. Whereprovided, retarding implant region 174 (not shown) may limit the extentto which layers 132, 140 extend into substrate 102. Otherwise, thedopant concentrations in layers 132, 140 and the conversion process maycontrol the thicknesses of layer 132, 140. As shown in FIG. 4 , in thisembodiment, forming pair of contacts 144, 146 includes forming metalcontacts or wires 160 that extend through STI 110 to upper surface 188of doped buried polysilicon layer 132. Metal contacts or wires 160 maybe formed using any now known or later developed contact/wire formingprocesses. In one non-limiting example, contacts or wires 160 may beformed by patterning a mask, etching opening(s) to the respective depth,and forming a conductor in the opening(s). The conductor may includerefractory metal liner, and a contact or wire metal. The refractorymetal liner (not labeled for clarity) may include, for example,ruthenium (Ru), tantalum (Ta), titanium (Ti), tungsten (W), iridium(Ir), rhodium (Rh) and platinum (Pt), etc., or mixtures of thereof. Themetal of contact or wire may be any now known or later developedcontact/wire metal such as but not limited to copper (Cu) or tungsten(W).

In any of the method embodiments described herein, isolation ring 170may be formed at any desired juncture, e.g., with STI 110. Whereisolation ring 170 includes a trench isolation, it may formed in asubstantially similar manner as STI 110.

Embodiments of the disclosure provide a structure 100 for providing apoly-resistor 130. As shown in FIGS. 1, 3 and 4 , structure 100 does notinclude oxide/STI under resistor 120, which improves the resistor'sthermal dissipation to substrate 102. The structure also allows improvedresistor density (with less area) by allowing stacked poly-resistorsbelow STI 110 and above STI 110—see additional resistor 242 above STI110 in FIG. 4 . Additional resistor 242 may be employed in anyembodiment. HR polysilicon layer 140 provides an isolation regionbeneath poly-resistor 130 that diminishes parasitic leakage of activedevices to substrate 102. See U.S. Pat. No. 10,192,779. Here, HRpolysilicon layer 140 also provides improved thermal conductivity frompoly-resistor 130 with reduced substrate coupling, and improvedfrequency response.

The method and structure as described above are used in the fabricationof integrated circuit chips. The resulting integrated circuit chips canbe distributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. “Optional” or “optionally” means thatthe subsequently described event or circumstance may or may not occur,and that the description includes instances where the event occurs andinstances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, “approximately” and “substantially”, are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged, such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.“Approximately” as applied to a particular value of a range applies toboth values, and unless otherwise dependent on the precision of theinstrument measuring the value, may indicate +/−10% of the statedvalue(s).

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the disclosure in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the disclosure. Theembodiment was chosen and described in order to best explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A structure, comprising: a shallow trenchisolation (STI) including a lower surface; a doped buried polysiliconlayer at least partially under the lower surface of the STI; a highresistivity (HR) polysilicon layer under the doped buried polysiliconlayer; and a pair of contacts operatively coupled in a spaced manner tothe doped buried polysilicon layer.
 2. The structure of claim 1, whereinthe HR polysilicon layer includes a noble dopant.
 3. The structure ofclaim 1, wherein the doped buried polysilicon layer under the STIincludes a boron dopant.
 4. The structure of claim 1, further comprisingan isolation ring bounding the doped buried polysilicon layer.
 5. Thestructure of claim 4, wherein the isolation ring is one of a trenchisolation and a doped well.
 6. The structure of claim 1, furthercomprising a retarding implant region below the HR polysilicon layer,within the HR polysilicon layer, or both within and below the HRpolysilicon layer.
 7. The structure of claim 1, wherein each contactincludes a doped monocrystalline semiconductor material extending besidethe STI, and each contact is operatively coupled to a lateral end of thedoped buried polysilicon layer.
 8. The structure of claim 7, whereineach contact contacts an upper surface of the HR polysilicon layer. 9.The structure of claim 1, wherein the doped buried polysilicon layerincludes a pair of vertical portions extending vertically along lateralsides of the STI, wherein each contact includes a doped semiconductormaterial operatively coupled to an upper surface of a respectivevertical portion of the doped buried polysilicon layer.
 10. Thestructure of claim 1, wherein each contact extends through the STI to anupper surface of the doped buried polysilicon layer, and each contact isin contact with the STI.
 11. A structure, comprising: a shallow trenchisolation (STI) including a lower surface; a resistor including a dopedburied polysilicon layer at least partially under the lower surface ofthe STI; a high resistivity (HR) polysilicon layer under the resistor;and a pair of contacts operatively coupled in a spaced manner to theresistor, wherein the HR polysilicon layer includes a noble dopant, andwherein the doped buried polysilicon layer includes a boron dopant. 12.The structure of claim 11, further comprising an isolation ring boundingthe doped buried polysilicon layer.
 13. The structure of claim 11,wherein each contact includes a doped monocrystalline semiconductormaterial extending beside the STI, and each contact is operativelycoupled to a lateral end of the doped buried polysilicon layer, whereineach contact contacts an upper surface of the HR polysilicon layer. 14.The structure of claim 11, wherein the doped buried polysilicon layerincludes a pair of vertical portions extending vertically along lateralsides of the STI, wherein each contact includes a doped semiconductormaterial operatively coupled to an upper surface of a respectivevertical portion of the doped buried polysilicon layer.
 15. Thestructure of claim 11, wherein each contact extends through the STI toan upper surface of the doped buried polysilicon layer, and each contactis in contact with the STI.